Gear glitch?

I have recently acquired Saotome Domaru +2 with overwhelm augment. According to all the sites it is supposed to give 2 tp per merit in overwhelm back whenever you ws from the front. However in my tests it only gives back 1 tp per merit, for a grand total of 5 tp in addition to ws's normal tp gain. Was there ever a mention of decreasing this value? Or is this just an error in the game? Has anyone else experienced this?